1. Field of the Invention
The present invention relates to an inkjet recording device provided with an inkjet recording head having a plurality of ink discharge holes, and employing a droplet modulating system for recording images. The present invention also relates to an inkjet recording method for controlling the inkjet recording device.
2. Description of Related Art
Conventional inkjet recording devices have employed recording systems capable of representing different tones (gradations) at each pixel, such as a multidroplet method and a droplet modulating method. The multidroplet method produces tones by varying the number of ink droplets ejected for each pixel. The droplet modulating method produces tones by changing the volume of the ink droplet (droplet diameter) ejected for each pixel.
Any deviation in the directions and amounts of ink droplets ejected from the plurality of discharge holes formed in the recording head may produce streaks in images that were meant to have uniform density variations, or unevenness in the density of the image. In other words, irregularity in the direction of ink ejection may cause deviations in the positions of dots formed on the recording paper, producing lines in the recorded image. Further, if there is any irregularity in the amount of ink ejected, the size or density of dots formed on the recording paper will be irregular, resulting in an uneven density in the recorded image.
One technique for resolving this problem involves recording the same line in multiple scans using different ink discharge holes for each scan. This technique, hereinafter referred to as the multipass recording method, ejects ink droplets from a plurality of nozzles to record the same line. Multipass recording attempts to produce a beautiful image by dispersing variations in the directions and amounts of ink ejected from each nozzle (attempts to produce a density that appears even to the human eye).
Examples of printers employing this technique include inkjet printers using a multidrop system or capable of multipass recording, such as that disclosed in Japanese patent No. 3176124. By using such an inkjet printer to record a single line with the multipass recording method, an image of better quality can be produced than when recording the same line with a single nozzle, as described above.
However, in the inkjet printer according to patent No. 3176124, all of the ink droplets ejected from the recording head have the same dot size. Since the same dot size is used, tones from light regions to dark regions are represented using a predetermined dot density (also called resolution). Therefore, it is necessary to use a relatively large dot size, which can lead to a graininess or rough texture in the recorded image.
Accordingly, an inkjet printer is proposed in Japanese patent No. 2963032 that is provided not only with a multidroplet system and a multipass recording capacity, but also with a droplet modulating capacity. With this capacity for regulating droplets, that is, varying the dot size of droplets ejected from the recording head, the inkjet printer according to Japanese patent No. 2963032 can reduce the graininess and rough texture in the recorded image.